Process for production of stencil tissue



Patented Apr. 17, 1951 PROCESS FOR PRODUCTION OF STENCIL TISSUE I of Delaware.

No Drawing. Application November 13, 1946, Se-

rial No. 709,424. 22, 1945 3 Claims.

I This invention relates to fibrous materials and .in particular to sheet materials suitable for use as duplicating-stencil tissue.

In Great Britain November Duplicating-stencil tissue is normally made from the fibres of Japanese mulberr bark, by a process in which the fibres are deposited from ,an aqueoussuspension on to a mesh to form a web. It is the principal object of the present invention to provide a duplicating-stencil tissue from materials which are freely available in this country. 1

Attempts to formsuitable sheet materials from regenerated cellulose staple fibres were unsuccessful owing to the difliculty of obtaining the desired degree of cohesion in the sheet material formed. Various methods of increasing the cohesion, for example by employing cellulose derivative adhesives such as methyl cellulose, and cellulose solvents such as complex compounds of copper with organic bases, also proved unsuccessful.

We have now found that a suitable sheet material can be provided in the form of a web of. regenerated cellulose staple fibres in admixture with adherent staple fibres of a thermoplastic derivative of cellulose.

The staple fibres are preferably all of the same denier and staple length, and the best results have been obtained by mixing the two kinds of staple fibre dry on a carding machine and collecting the resulting web off the doifin cylinder of the carding machine on to a rough surfaced paper. The web obtained in this way may be folded in two to give a heavier and more even web. Naturally the proportion of cellulose derivative fibres in the mixture must be sufficient to bond the web into a'coherent sheet. The best results have been obtained using equal proportions of the two kinds of fibre.

To render the cellulose derivative fibres adherent and convert the web into a coherent sheet,

it may be pressed between sheets of fabric at an ity regenerated cellulose.

- mersed in a solution containing 25 parts of indus- I webs obtained by pressing. in the presence of .water alone are apt to be uneven and fluffy. At-

tempts to obviate this difiiculty by incorporating a plasticiser with the cellulose derivative fibres were found to cause sticking of the web to the enveloping layers of fabric. This difiiculty of adhesion to the layersof fabric was also found when using, instead of water, an active solvent such as acetone, dioxane, or' methylene ethylene ether, diluted with up to about its own volume of water, or a potential solvent for cellulose ace tate, that isa liquid which becomes a solvent at elevated temperatures, for example methanol, ethanol or isopropanol, diluted with about 25%, by volume of Water. Satisfactory results, however, were obtainedby the use of very much more dilute solutions of an active solvent for'the cel for pressing will be between and 150 C.

The invention may be illustrated as follows:

Staple fibres of cellulose acetate of 3% denier and 1% inch staple length,.together with regenerated cellulose staple fibres produced by the viscose process and of the same denier and staple length, are fed in equal proportions by weight to a carding machine. Theresulting web is collected 01f the dofiing cylinder on to a rough surfaced paper, folded in two, and sandwiched between two layers of a woven fabric of .high tenactrial alcohol and 75 parts of water, the parts bein by volume, and then pressed between two layers of cotton fabric each backed by two layers of woolen fabric, in a steam heated platen press, for 3 minutes at C. under a pressure of 40 to 50 pounds per square inch. In this way a web is formed in which the cellulose acetate fibres are bonded together but which can readily be peeled off from the enveloping fabric. The web weighs about 0.9? ounce per square yard and is approximately 0.07 mm. in thickness. It is even in thickness, has a smooth surface free from fluffiness and is suitable for use as a duplicatingstencil tissue.

It is an advantage of the process of the invention that it does not involve subjection of: the staple fibres to severe mechanical action tending 2,548,971- UNITED STATES 'eAT NT OFFICE The assembly is imto'shorten the fibres, such as occurs in the production of pulps for paper-production. The avoidance of such mechanical action coupled with the adherence of the thermoplastic fibres, enables products of high strength to be obtained.

The denier and staple length of the fibres used may be varied within certain limits. Thus, fibres of denier less than 3 for example fibres of denier 2, 1, or even less than 1, can be employed. The denier can be somewhat higher than 3 /2, e. g. 4, but should not be substantially higher than about 5. The staple length may range from about 1 inch or even less to about 2 inches.

The regenerated cellulose :fibres have been described as made by the viscose process. Regenerated cellulose fibres made by other methods may, however, be employed. For instance the fibres may be made .by the cuprammonium method or by the saponification of cellulose ester fibre, especially high tenacity cellulose ester fibre obtained as the result of stretching dry-spun cellulose acetate fibre, preferably in the form of yarns of continuous filaments, to a considerable degree, for example to 5 to times its-original length-in steam or hot water.

cellulose fibre) or after spinning (as, for example,

in the steam-stretching of dry-spun cellulose acetate fibre), enable fibres to be produced of "high tenacity, e. g. 2 to 4 or 6 or more grams per denier, and of low denier, e. g. between 2 and 1 oreven less than 1. 'Very strong, thin tissues can be made when the regenerated cellulose fibres are made by such a process.

(Instead of cellulose acetat fibres, staple fibres of other thermoplastic derivatives of cellulose maybe used. Examples of such derivatives are other carboxylic acid esters of cellulose such as cellulose propionate, cellulose ibutyrate, cellulose acetate stearate, cellulose acetate palmitate, and cellulose acetate laurate; and others of cellulose .such as ethyl cellulose, propyl cellulose, and

benzyl cellulose. The staple fibres may be obtained by cutting a multi-filament yarn obtained :by a dry-spinning operation from a solution of the cellulose derivative; or by stretching such a dry-spun multi-filament yarn in steam or hot water to produce a high tenacity yarn, and cutting this intostaple fibres; or by cutting into staple fibres a multi-filamem yarn of the derivative of cellulose, formed by a wet-spinning operation.

Th invention includes the provision of sheet materials of the structure referred to above for purposes other than for use as duplicator-stenoil tissue, .e. g. for use in electrical insulation and :in protecting highly polished surfaces against scratching.

Having described our invention, what we desire to secure byLetter Patent is:

1. Process for the production of a sheet material which is suitable for use as a duplicating stencil tissue, which comprises forming a web of a weight of at most 1 oz. per square yard of a mixture of regenerated cellulose staple fibers and cellulose acetate staple fibers, moistening said web with a softening agent selected from the group consisting of a 20-30% aqueous solution of a saturated aliphatic alcohol of from 1 to 3 carbon atoms, acetone diluted with 8 to 9 times its volume of water and dioxane diluted with 8 to 9 times .its volume of water, and pressing said moistened web at a temperature of 120-150 C. between layers of fabric whereby the cellulose acetate fibers are bonded one to another Without being stuck to the fabric layer.

2. Process for the production of sheet material which is suitable for use as a duplicating stencil tissue, which comprises forming a web of a weight at most 1 oz. per square yard of a mixture of regenerated cellulcse staple fibres and cellulose acetate staple fibres, moistening said Web with a 20-30% aqueous solution of a saturated aliphatic alcohol-of 1 to 3 carbon atoms and pressing said moistened web at a temperature of l20-150 C.

between layers of fabric whereby the cellulose acetate fibres are bonded one to another without being stuck to the fabric layer.

3. Process for the production of sheet material which is suitable for use as duplicating stencil tissue, which comprises carding a mixture of regenerated cellulose staple fibres and cellulose acetate staple fibres into a Web of a weight at most 1 oz. per square yard, moistening said web with aqueous ethyl alcohol of 20-30% strength and pressing said web at a temperature of 120-150 C. between layers of fabricwherebythe cellulose acetate fibres are bonded one to another without being stuck to the fabric layer.

ERNEST LESLIE GREENYVOOD. FREDERICK WILLIAM HUGHES.

ALBERT WILLIAM MORIJEDGE-I-IADFIELD.

REFERENCES CITED The following references are of record in the file of this patent: 

1. PROCESS FOR THE PRODUCTION OF A SHEET MATERIAL WHICH IS SUITABLE FOR USE AS A DUPLICATING STENCIL TISSUE, WHICH COMPRISES FORMING A WEB OF A WEIGHT OF AT MOST 1 OZ. PER SPUARE YARD OF A MIXTURE OF REGENERATED CELLULOSE STAPLE FIBERS AND CELLULOSE ACETATE FIBERS, MOISTENING SAID WEB WITH A SOFTENING AGENT SELECTED FROM THE GROUP CONSISTING OF A 20-30% AQUEOUS SOLUTION OF A SATURATED ALIPHATIC ALCOHOL OF FROM 1 TO 3 CARBON ATOMS, ACETONE DILUTED WITH 8 TO 9 TIMES ITS VOLUME OF WATER AND DIOXANE DILUTED WITH 8 TO 9 TIMES ITS VOLUME OF WATER, AND PRESSING SAID MOISTENED WEB AT A TEMPERATURE OF 120-150* C. BETWEEN LAYERS OF FABRIC WHEREBY THE CELLULOSE ACETATE FIBERS ARE BONDED ONE TO ANOTHER WITHOUT BEING STUCK TO THE FABRIC LAYER. 